CAVITY
About 85 species in North America make nests using cavities, birdhouses, gaps in structures or holes found in tree hollows, telephone poles, abandoned buildings and more.

Of the birds that use nest cavities, most woodpeckers (Picidae) including the northern flicker [Colaptes auratus] and red-naped sapsucker [Sphyrapicus nuchalis] tend to be the species that do the hard work of excavating many of the tree cavities. Fewer birds excavate their own holes in trees. But of those that do, the woodpeckers are by far the best known. The cavity using opportunists include bluebirds (Sialia), chickadees (Paridae), house sparrows, house wrens [Troglodytes aedon], nuthatches (Sitta), the bridled titmouse [Baeolophus wollweberi], violet-green swallows [Tachycineta thalassina], many parrots, and even some small owls such as the northern saw-whet owl [Aegolius acadicus]. Red-cockaded woodpeckers nest in cavities that can take years to construct in a living tree. They live in groups and will have as…